1. Field of the Invention
This invention pertains to control devices for prime movers, and more particularly, to electronic governors for speed control to one of two or more connected, independently powered vehicles.
2. Description of the Prior Art
Where powered vehicles are used to move great loads, or where such vehicles operate over rough or uneven terrain, two or more such vehicles, each with its own engine and transmission, are often linked together to form one unit for purposes of transport of the load. A first problem encountered in such an arrangement is control: the driver of the linked vehicles, seated on one of the powered vehicles (hereinafter designated the master vehicle), must be able to control ground speed of the overall unit, for example, through control of the engine speed of the other powered vehicles (hereinafter designated as slave vehicles) which are linked together with the master vehicle. It is preferable that this control be automatic insofar as possible, with possible manual overrides, so that the driver may direct his attention to manual control of the master vehicle.
Earlier inventions for the control of one or more motorized slave vehicles from a motorized master vehicle include the disclosure in U.S. Pat. No. 2,140,109 to Kellar, wherein the master vehicle is directly controlled by the operator throttle pedal and a mechanical link therefrom controls the throttle setting of the slave vehicle engine. The more recent U.S. Pat. No. 3,804,191 to Golan teaches the simultaneous electrical control of master and slave engines and simultaneous gear change of the two vehicles; anti-stall control apparatus causes the slave transmission to downshift if the slave wheel speed drops below a certain value and is used primarily to control slip of the vehicle wheels.
The use of magnetic pickups or like devices to determine wheel speed or overspeed and the utilization of such devices in control circuits for controlling the wheel speed in common in the prior art. The earlier U.S. Pat. Nos. 3,060,602 to Buttenhoff, 3,257,612 to Gorrill et al. and 3,776,355 to Scherenberg teach the use of such monitoring devices and control circuits. The patent to Scherenberg, for example, teaches the use of means for monitoring wheel speeds on a vehicle wherein excess wheel slippage provides a signal which acts to reduce the engine output.
An earlier wheel slip control invention is disclosed in the U.S. Pat. No. 3,130,805 to Carter, which also makes use of magnetic pickup devices for monitoring the wheel speeds of tractor and trailer vehicles with only the tractor vehicle being powered, and control of the tractor throttle is through electro-magnetic means controlled by said pickup devices.
The U.S. Pat. No. 3,776,322 to Misch teaches the use of electronic apparatus for slip control of driven versus undriven axles on a single vehicle.
The prior-mentioned patents teach the use of circuitry which is primarily, or entirely, analog. An exception to the parade of analog wheel speed control inventions is disclosed in the U.S. Pat. No. 3,802,188 to Barrett and comprises a digital electronic governor. Barrett uses an up-down counter to monitor and compare actual wheel speed with a desired wheel speed, each speed being represented by a pulse train of variable frequency. The Barrett approach is quite complex as it uses iteratively weighted averages of the prior and present pulse period difference to generate commands to the governor.